Modern vehicles are in many instances equipped with a driving speed controller with the aid of which the speed of the vehicle is controlled to a predetermined desired value pregiven by the driver. An example for a road speed controller is known from U.S. Pat. No. 4,884,203. Road speed controllers of this kind are complex and consume a certain portion of the available resources of a control apparatus (most of all of the computation time of the computer). The control apparatus is for controlling the drive unit of the vehicle. In some applications, the implementation of such a road speed controller can lead to problems.
The same applies also to road speed limiters which limit the speed of a vehicle to a maximum speed adjustable by the driver. An example for such a function is disclosed in U.S. Pat. No. 5,854,989.
A drive slip controller is known from German patent publication 197 34 112 wherein continuously the output torque is determined which is transmittable from the wheel to the roadway. If an instability occurs at least on one drive wheel of the vehicle, then the output quantity (preferably a desired torque value) of the drive slip controller, which is set to maximum value, is reset to a value corresponding to the maximum transmittable output torque. For a continuing slippage, this desired value is successively reduced and for lessening or vanishing drive slippage, the desired value is successively increased until the maximum value is again reached. If drive slip occurs anew, the desired value is set again to the quantity which represents the maximum transmittable value.
An engine drag slip control is disclosed in U.S. Pat. No. 5,676,111. There, a desired torque value is determined on the basis of the wheel behavior of at least one drive wheel and this desired torque value functions to adjust the drive unit. Here too, the desired value is successively increased when there is a tendency for blocking and for a lessening blocking or for a vanished tendency to block, the desired value is again reduced to the output value which is here preferably the value 0.
U.S. Pat. No. 5,558,178 discloses the determination of a driver desired torque on the basis of the accelerator pedal position and the engine rpm. A resulting desired torque is determined in the context of a maximum and minimum selection from this driver desired torque and the desired torque of the engine drag torque controller and the desired torque of the drive slip controller. The torque of the drive unit is adjusted in dependence upon this resulting desired torque.
The realization of a road speed limiter function (FGB) and/or a road speed controller function (FGR) via the control systems for the control of the drive slip or of the engine drag torque, which are anyway available, reduces the complexity of the software of the control unit of the drive unit because the complex road speed limiter (FGB) and/or road speed controller (FGR) can be omitted.
Notwithstanding the omission of a separate road speed limiter and/or road speed control function, a reliable, satisfactory limiting and/or control of the road speed of the vehicle is achieved.
Special advantages are presented when an additional road speed limiter control apparatus or road speed control apparatus is eliminated and thereby considerable costs are saved.
It is especially advantageous that the resource requirement, which is increased by a conventional complex road speed limiter and/or road speed controller, is omitted and the expansion of the resources is unnecessary which would be required for the use of such a function.
For a drive slip controller, which acts also on the wheel brakes, it is especially advantageous that a road speed limiter and/or road speed control with brake intervention is realized with additional complexity and the speed limiting and/or speed control is improved in this manner.
It is further advantageous that, to realize the road speed limiter (FGB), one can make use of the function of the road speed controller (FGR) so that this additional function can be realized without additional complexity.